The present paper presents a spatio-temporal characterization of the natural grasslands from Bucegi Natural Park using remote sensing resources such as radiometric information from the multispectral satellite images – S10 MERIS of ENVISAT, and aerial high-resolution orthophotos, to provide the Normalized Difference Vegetation Index (NDVI) of the natural grasslands and their delineation. The sampled data were georeferenced in stereographic 1970 coordinate system and were used to create thematic layers in GIS environment and to perform statistic inferences. A procedure that correlates and reclassifies radiometric data was developed using previous terrestrial observations and thematic information from the satellite images of the studied area. The multispectral images photointerpretation allowed the generation of thematic maps with attributes from database and radiometric information between 2010 and 2011 vegetation seasons, which were correlated using multi-temporal archives of NDVI values. In our study based on two subsequent years of satellite observations in the vegetation seasons, a NDVI threshold of 0.45 seemed to be appropriate to be considered as a start of season in the Bucegi Natural Park. NDVI weighted averages were computed based on available pixels for each month of the studied years as follows: 0.38 in March, 0.54 in April, 0.60 in June, 0.75 in July, 0.74 in August, and 0.71 in September. The lowest NDVI values were recorded in the northern part of Bucegi Natural Park, while the southern grasslands presented higher values correlated with earlier start of vegetation growth.